1. Field of the Invention
This invention relates to a rotational bearing system which is suitably applicable, for example, to a hard disk head access mechanism or the like.
More specifically, this invention concerns a rotational bearing system with a ball bearing for rotatably supporting a shaft or a housing, the bearing system including means to excite a shaft or a housing, whichever is on the stationary side, in vibration to reduce the frictional resistance of the bearing to a marked degree.
2. Description of the Prior Art
Shown in FIG. 18 is the construction of a head access mechanism in a conventional hard disk device, including a swing arm 5 rotatably mounted on an arm bearing assembly 4 for rotational movements relative to a magnetic memory medium or a hard disk 3 mounted on a base 2. A magnetic head 7 is mounted on the fore distal end of the swing arm 5 through a head suspension 6.
A voice coil motor 8 is mounted on the rear end of the swing arm 5 away from the magnetic head 7. The swing arm 5 is rotationally driven according to a tracking control signal which is supplied to the voice oil motor 8, moving the magnetic head 7 across the recording tracks formed on the magnetic memory medium 3, for making an access or for a tracking action.
As shown in FIG. 19, the arm bearing 4 has its housing 15 rotatably supported on a fixed shaft 13 which is planted on a base member 14 by means of a fitting screw 12, through ball bearings 14 which are arranged around the fixed shaft 13. The swing arm 5 is fixedly mounted, for example, on the upper end of the housing 15.
With the hard disk head access mechanism of the above-described construction, in case the track pitch between the respective recording tracks on the magnetic memory medium 3 is minimized to increase the recording density, as a matter of fact the accuracy of controlling the position of the magnetic head 7 has to be extended to a range of fine movements of the order of submicrons.
For fine and high-speed control of the position of the magnetic head 7, it is important to reduce the frictional resistance of the ball bearings 14 of the arm bearing 4. For instance, if the ball bearings 14 have a large frictional resistance, correct tracking control of the magnetic head 7 becomes difficult due to lack of linearity between the tracking servo signal which is supplied to the voice oil motor 8 for a fine displacement of the magnetic head 7 and the actual magnetic head displacement.